Linting and dusting are terms used to define the tendency of a paper surface to shed loose and weakly bonded particles and accumulate these on the blanket during offset printing.
Linting is a fibre, fibre fragment, ray cell or vessel element removal phenomenon related to both pulp and paper properties as well as printing conditions. Dusting is the result of loss of filler or other fine materials that are not firmly attached to the paper surface. When removed during printing, linting and dusting materials easily accumulate on the printing blanket, especially in the first printing unit when multiple printing units are used.
The mechanism of linting is not entirely understood and solving problems related to linting may be difficult processes. The mechanism of linting can generally be ascribed the inter-fibre bonding strength on the paper surface. That is to say, lint and dust are removed from the surface of the paper when the external forces exceed the forces holding the sheet together.
Picking is another aspect when it comes to the printability of paper. Picking stands for the pulling out of fibres or small clusters of fibres. Picking may in extreme cases result in sheet delamination, whereby large uniform areas are lifted from the paper surface. Picking occurs when the split resistance of the ink and hence the stress perpendicular to the paper surface exceeds the local strength of the paper surface at the outlet of the nip. Picking may result in linting.
Material removed from the paper surface consists mostly of poorly fibrillated fibres, non-fibrous cell materials (such as ray cells, vessels, bagasse pith etc) as well as fibre fragments, fines and debris. It is well-known that coarse and stiff fibres require a higher energy input during refining in order to minimize linting. The energy input hence is probably one of the more important parameters affecting linting.
Surface sizing is a known procedure for alleviating the linting tendency of newsprint. The linting problem cannot, however, be regarded solely as a papermaking problem. Printing press variables have a strong influence on paper linting performance and must by carefully controlled. Important press room factors include edition size, web lead configuration through the press (departure angle etc.), ink properties (viscosity and tack) and the fountain solution (quantity and quality). Linting can also be caused by an incorrect ink/water balance. From earlier studies, it can be concluded that several press variables often contribute to linting.
Linting results in deterioration of the print quality to the point where the press must by stopped and cleaned. This cleaning process is both tedious and costly. The linting tendency of paper can therefore have a strong effect on pressroom efficiency, particularly in high volume printing operations such as newspaper production. The continued trend towards increased use of offset printing in high volume multi-colour printing operations has made linting a considerable economic problem and a source of frequent customer complaints. Consequently, there exists a need for improved sheets of paper with reduced linting and dusting propensity and additionally compositions for affecting said improvements.